1. Field of the Invention
The present invention relates to a test socket used for testing electrical characteristics of semiconductor devices.
2. Discussion of Background
In accordance with advancement of functions and miniaturization of electronic equipments, the number of outer connecting terminals of semiconductor devices are increased, a density of semiconductor device becomes high, and semiconductor packages such as a ball grid array (BGA) type, which is formed by arranging outer connecting terminals on a lower surface of a semiconductor device in a grid-like form, and a chip scale package (CSP) type are increasingly used instead of a QFP type formed by arranging outwardly drawn-out connecting terminals, or an SOP type semiconductor package. When such a semiconductor package is delivered, electrical performance tests of the semiconductor device are conducted, wherein a tests socket, served as an interface connecting a tester, e.g. a computer, for conducting the performance tests to outer connecting terminals of the semiconductor device, is required.
FIG. 13 illustrates an example of a conventional test socket for testing a QFP type semiconductor package or an SOP type semiconductor package, formed by outwardly drawing out connecting terminals, wherein probes 1, formed by punching out an elastic member to have a predetermined shape, and a housing 11 for holding and fixing the probes 1 fabricate the test socket. In order to test, a semiconductor package 14 is supported by a seat 13, tips of the probes 1 are in contact with outer connecting terminals 14a, such as a lead, drawn out of the semiconductor package 14, and a securing jig 12 pushes the outer connecting terminals 14a toward the tips, whereby the outer connecting terminals 14a are electrically connected with the probes 1, and a predetermined test signal is transmitted to and received from an electric circuit of the semiconductor device, located inside the semiconductor package 14 through the probes 1 and the outer connecting terminals 14a. 
In this test socket, the probes 1, being in contact with the outer connecting terminals 14a, are arranged on four sides or two sides in a periphery of the semiconductor package 14. The probes 1 are formed to have a bent shape, for example, a U-shape, and have tip portions 1a, being in contact with the outer connecting terminals at ends thereof and connecting terminals 1b connected to the tester and located in a housing at the other ends, wherein when the outer connecting terminals 14a are pressed to the tip portions 1a, a part of the U shape is bent and contacting force is obtained by counterforce from the part.
Further, FIGS. 14a and 14b respectively are a cross-sectional view of a CSP type semiconductor package, formed by arranging outer connecting terminals 14a on a back surface of a semiconductor device in a grid like form, and a plan view, viewed from the back surface. The outer connecting terminals 14a and aligning electrodes 18 are arranged on the back surface of the semiconductor device 14 in a grid-like form. Accordingly, it is difficult to arrange the probes 1 of the conventional test socket. Therefore, a test socket having pin-like probes 1, for example, illustrated in FIG. 15, is also used for a CSP type semiconductor package. In the figure, numerical reference 1 designates a probe; numerical reference 11 designates a housing; numerical reference 14 designates a semiconductor package; numerical reference 14a designates an outer connecting terminal; numerical reference 15 designates a socket; numerical reference 16 designates a circuit board; and numerical reference 17 designates a connecting pin for connecting with a testing equipment. In thus constructed test socket, the probes 1 formed like a pin, named Pogopin, is provided. Therefore, it is possible to arrange the probes 1 in correspondence with a large number of outer connecting terminals 14a, formed on a lower surface of a semiconductor device, so that a density of the probes 1 is high.
Because the density of the pin-like probes 1 used in the test socket is high, and the outer connecting terminals cannot have elasticity, which is achieved by bending to have a U-shape as in the probes 1 of the test socket for QFP type semiconductor packages and so on, which packages are arranged so that their outer connecting terminals are outwardly drawn out, a structure, for example illustrated in FIG. 16, is adopted to apply pressure. In FIG. 16, numerical reference 101 designates a cylinder for guiding a tip 100a of a plunger, in contact with outer connecting terminals 14a of a semiconductor package, and the plunger 100 to enable reciprocal motion; and numerical reference 102 designates a coil spring for securing a contact pressure and a stroke of the plunger. The tip 100a of the plunger is in contact with an outer connecting terminal 14a such as a solder ball. In order to increase a contact area, there is a case that the tip is shaped like a recess. The pin-like probe 1 works such that the plunger 100 is backwardly moved by a contact along with pressure between the tip 10a of the plunger and the outer connecting terminal 14a, e.g. a solder ball, of the semiconductor package 14, the contact pressure is obtained by counterforce of the coil spring 102, and simultaneously, the tip 100a of the plunger breaks an oxide coating, formed on a surface of the outer connecting terminal, so as to be in contact with a new metallic surface inside the outer connecting terminal, whereby an electric connection is obtainable.
Further, FIGS. 17a and 17b are cross-sectional views of a probe for a conventional test socket for another CSP type semiconductor package, disclosed in Japanese Unexamined Patent Publication JP-A-7-272810. The test socket has a floating plate 21, constantly pushed in an upward direction by a spring (not shown), whereby when a semiconductor package 14 is installed and pushed, the floating plate 21 is downwardly moved. The probe 1 is shaped like a pin, and a twisted lead plate 24 is located in addition to a contacting part 25, being in contact with the outer connecting terminal 14a. As illustrated in the figures, when the outer connecting terminal 14a further pushes the contacting part 25 from a state that the outer connecting terminal 14a is in contact with a contacting surface 25b having a taper-like inner periphery of the contacting part 25, a rectangular lead hole 25a of the contacting part 25 is guided by a piece 24a of the twisted lead plate 24 and applied with a rotating force in a direction of an angle of the twisted lead plate. Accordingly, the contacting surface 25b having a taper-like inner periphery 25b is kept to be in contact with the outer connecting terminal 14a, and the outer connecting terminal 14a is slid on and rubbed with the contacting surface 25b by the rotating force while keeping the contacting surface 25b having a taper-like inner periphery in contact with the outer connecting terminal 14a, whereby an oxide coating is destroyed and dust is expelled, whereby electrical connection is obtainable without spoiling the outer connecting terminal 14a. 
However, the probe 1, pressing the tip 100a of the plunger by the cylinder, made large scars to the outer connecting terminals 14a, e.g. solder balls, of the semiconductor package. Therefore, a void is caused at time of mounting the outer connecting terminals to a printed circuit board and so on by melting the outer connecting terminals in use of reflow of solder, whereby a defect of blowhole is caused.
Further, as illustrated in FIG. 18, when remains 30 of solder adheres to and are deposited on a tip of a probe, the remains are oxidized in the atmosphere, and a contact resistance is increased by a coating of an oxide film 30a, there were problems that a semiconductor device could not be tested, and a function of the socket could not be demonstrated.
Further, the probe having a rotating mechanism, disclosed in the above-mentioned Japanese Unexamined Patent Publication JP-A-7-272810, easily produced an alloy, and the alloy was welded because large shear force is applied when the probe is in contact with the new surface of the solder, and a temperature of the contacting surface is locally increased. Further, there were problems that a contact resistance was increased by the coating of the oxide film, the semiconductor device could not be tested, and a function of the socket could not be demonstrated.
Further, it was necessary to spend a very long time and much labor for exchanging probes, selected as having high contact resistances or connection failures out of a large number, e.g. several hundreds, of the pin-like probes arranged in a grid-like form. There was a problem that a cost becomes very high when a socket itself was changed because a unit price of the above-mentioned pin-like probe is high.